Exposure to ultraviolet radiation can cause aging of cells and mutagenic changes to cells within the human body. Solar ultraviolet radiation is present in the rays of the sun, resulting in repeated and regular exposure by an eye to UV-A and UV-B radiation. The human ocular system does not develop a tolerance to repeated ultraviolet exposure.
The acute effects of repeated and regular UV-A and UV-B radiation exposure include conjunctivitis and photokeratitis, a corneal inflammation reaction. Exposure to UV-A and UV-B radiation also contributes to early formation of cataracts, especially in persons with blonde hair and blue eyes living in sun belt zones of the United States.
It is important for the cornea to have an optically smooth surface for the formation of a sharp visual image on the retina. Repeated exposure to ultraviolet radiation can result in the swelling or shrinking of groups of corneal epithelial cells. This can lead to visibly recognizable stippling or irregular mosaic granulation of the corneal surface. With UV-A and UV-B exposure greater than the threshold for photokeratitis, surface epithelial cells exhibit nuclear fragmentation, mid-epithelial cells exhibit vacuole formation, and basal cells exhibit inhibition of mitosis and clouding of the corneal stroma occurs.
A healthy cornea prevents exposure by the retina to ultraviolet radiation. When the cornea is damaged or replaced, the eye becomes extremely sensitive to ultraviolet radiation and the retina is exposed to ultraviolet radiation.
The retina is a delicate nervous membrane upon which the images of external objects are received. A healthy retina is soft, semitransparent, and has a purple tint. Upon exposure to ultraviolet radiation it becomes clouded, opaque, and bleached. Prolonged exposure to ultraviolet radiation causes damage to the retina.
High-energy visible light (HEV light) is high-frequency light in the violet/blue band in the visible spectrum, between 380 and 500 nm. HEV light is thought to be a cause of age-related macular degeneration resulting from damage to the central portion of the retina. Although it has not been conclusively shown to cause retinal damage, absorption of HEV light has been shown to cause a reversal in the natural visual cycle, resulting in a greater potential for oxidative damage to the eye. Thus, the lens of the eye and the retina may show irreversible changes induced by prolonged exposure to moderate levels of HEV light. Additionally, following an intraocular lens implant, the retina becomes particularly sensitive to HEV light exposure.
A need exists for an ophthalmic solution that can be applied to the eye to absorb ultraviolet radiation and to filter out HEV light.